Measurement of ThioTEPA and Its Metabolite TEPA in Plasma and Cerebrospinal Fluid by Turbulent Flow Chromatography-Tandem Mass Spectrometry

N,N′,N′′-Triethylenethiophosphoramide (thioTEPA) is a polyfunctional, organophosphorus alkylating agent that has been a primary treatment of multiple solid malignancies for many years and more recently as part of conditioning regimens prior to hematopoietic stem cell transplantation for a variety of hematologic malignancies. In vivo, thioTEPA is quickly metabolized to N,N′,N″-triethylenephosphoramide (TEPA). ThioTEPA and TEPA have similar alkylating activity and both exhibit outstanding central nervous system penetration. Therefore, it is possible and desirable to monitor both compounds in plasma and cerebrospinal fluid (CSF). This chapter describes a method to measure both compounds simultaneously. ThioTEPA and TEPA are extracted with solvent from plasma and CSF by the addition of deuterated internal standards prepared in methanol. Chromatographic separation is attained using a C18 column and mass spectrometry which is performed in the positive ion mode. Herein, we describe a fast, accurate, and sensitive assay to quantify both compounds in plasma and CSF by turbulent flow LC-MS/MS which allows for fast and accurate therapeutic drug monitoring and timely dose modifications.